FI91642B - Cationic lignin which can be used as a flocculating agent and method for purification of waste water - Google Patents

Description

91642

This invention relates to cationic lignin useful as a flocculant and to a process for treating wastewater.

Lignin is a natural polymer that is produced in large quantities as a by-product of the wood processing industry. When cellulose is isolated, lignin enters waste liquors, from which the heat obtained from wet combustion after concentration is an energy advantage (sulphate process). Lignin can be precipitated from the waste liquor by acidification as well as the black liquor can be purified and fractionated by ultrafiltration, thus allowing chemical modification of the ultrafiltration fractions.

15 Lignin isolated from sulphate waste liquor has an average molecular weight of about 1500 to 5000, but can be fractionated, for example, by ultrafiltration or solvent treatment of black liquor so that the molecular weight distribution is greater than 5000 at 50%.

In the past, cationic lignins have only been prepared from acid-precipitated lignins and have been poorly tested in wastewater treatment (see, e.g., U.S. Patent Nos. 4,775,744 and 3,718,639).

In the preparation of cationic lignin according to the invention, the ultrafiltered fraction of the waste liquor has the advantage that the acid precipitation step of lignin which has been included in the previous methods is omitted. Thus, the process in which the cationic lignin is prepared from the above-mentioned material also offers a more economical alternative to the previously known processes. Thus, a cheap cationic flocculant is obtained, which makes the treatment of large amounts of wastewater meaningful.

Ultrafiltration of black liquor also has the advantage that ultrafiltration avoids the small-molecular fraction of black liquor and gives a fraction advantageous for flocculation of wastewater colloidal substances with a molecular weight of 2,91642> 20,000. The ultrafiltered fraction thus provides a better starting material for wastewater treatment. The advantages of ultrafiltration also include the natural concentration of black liquor, in which case the concentration required for cationization 5 is already achieved by this procedure.

In the present invention, the hydroxyl groups of lignin are modified with epoxyammonium or chlorohydrin ammonium salts in "Preparation and Testing of Cationic Flocculants from Kraft Lignin", ACS Symposium Series 397, 195th National Meeting of the American Chemical Society, Toronto, Ontario, Canada, June 5-11, 1988. , as shown in the following diagram:

NaOH

lignin-OH + CH 2 CHCl 3 N 2 C 2 Cl 9 'slow O glycidyltrimethylammonium chloride lignin-OCH 2 CHCH 3 N 2 FCH 2 JClCl GTAK-reagen.si lii

λ. OH

NaOH

S NaCl + O- fast ^ CH2CHCH2N® (CH3) 3Cl2, + NaOH (chlorohydrin reagent)

:. 25 I I

QJOH N (3-chloro-2-hydroxypropyl) trimethylammonium chloride In U.S. Patent No. 3,718,639, lignin amines 30 are prepared by reacting lignin in the same manner with the reaction product of epichlorohydrin and a tertiary amine. This patent does not specify the yield of the epoxy reagent associated with the hydroxyl groups. The aforementioned "Preparation and Testing of 35 Cationic Flocculants from Kraft Lignin" discloses that with 91642 3 glycidyltrimethylammonium chloride, this yield can be greater than 50% for purified typical softwood soup isolated from the black-head of coniferous soup (Indulin AT, manufactured by Westwaco Corp.). In contrast, N- (3-chloro-2-hydroxy-5-cipropyl) trimethylammonium chloride (GTAK-HCl reagent) did not achieve a reagent yield of more than 50%.

It has now surprisingly been found that starting from the black-head ultrafiltered fraction with GTAK-HCl reagent, more than 50% reagent yield is obtained. Reacting the black-10 head alkali lignin with the GTAK-HCl reagent also provides the advantage that the reagent neutralizes the alkali contained in the black liquor. It is essential to achieve a high reagent yield that the progress of the reaction is monitored by periodically determining the flocculation efficiency of a sample taken from the reaction mixture with respect to a colloidal silica standard.

At the same time, the excess NaOH relative to the chlorohydrin reagent converted to the epoxy reagent is kept low (about 10% of the reagent volume) by continuously neutralizing some of the NaOH.

The invention relates to a cationic lignin suitable for use as a flocculant, characterized in that it is prepared from an ultrafiltered fraction of black liquor by first ultrafiltrating the black liquor and then cationizing the resulting ultrafiltered fraction with glycine. . With diethylammonium chloride or N- (3-chloro-2-hydroxypropyl) trimethylammonium chloride.

In a preferred embodiment, the lignin can also be crosslinked with formaldehyde, whereby the network of the lignin molecule expands all the way to gelation. It has been found that as crosslinking increases, the optimum blocking dose of the corresponding cationic lignins with respect to colloidal materials decreases. At the same time, the consumption of the cationization reagent can be reduced without a decrease in the nitrogen contents of the cationized lignins.

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The effect of cationic polymers on wastewater is known to adhere to the surface of negatively charged colloidal particles contained in the wastewater alone or with inorganic coagulants and neutralize the surface charge as well as remove the interparticle removal force. In this case, the colloidal components precipitate.

If a high molecular weight (MP several million) linear, cationic, anionic or neutral water-soluble polymer is present in the flocculation dose, the long flexible polymer chains connect the contaminant particles into bundles that settle as large flocs.

Also, in the typical pH range of wastewater (pH 6-8), iron and aluminum salts contain cationic molecular species that neutralize the negative surface charges of colloidal particles and rapidly polymerize into hydroxyl gels, while enclosing the harmful fraction. Often, however, coagulant doses are high and the resulting sludges do not settle well.

It is an object of the present invention to reduce the amount of inorganic sludges and to improve their settling and concentration properties. This is generally accomplished with composite flocculants that include a cationic polyelectrolyte, an inorganic coagulant, and a mahdollisesti 25 potentially neutral or anionic high molecular weight polymer. It has now been found that in several combination doses, the cationic polyelectrolyte can be replaced by cheaper cationic lignin without compromising flocculation efficiency.

Several experiments with phosphorus-containing effluents show that the cationic polyelectrolyte together with the Al and Fe salts not only remove the colloidal solid but also significantly reduce the amount of phosphorus. In these cases, the high cost of the cationic polyelectrolyte often precludes the use of a combination dose. It has now been found that 91642 5 good results can be obtained when the cationic polyelectrolyte is replaced by cationic lignin. When replacing an expensive cationic polymer in a component dose with a cheaper cationic lignin, the removal of the phosphorus-containing colloidal fraction also becomes economical.

The flocculation efficiencies of cationic polyelectrolytes and cationic lignins can be compared by preliminary tests. In the vessel test, the colloidal dispersion is mixed with different maximum flocculant dosages, with the lowest residual turbidity in the series after settling of the precipitate 10 indicating the optimum flocculation dose. Tests performed with a dispersion analyzer show relative floc size. By performing this test at different mixing speeds, the resistances of the flocs can be compared. Microcrystalline silica and microcrystalline cellulose have been used as colloidal standard dispersions in the vessel test and in the analyzer tests. A predetermined time has been used as a pre-test for flock leachability, with the colloidal dispersion or wastewater sample seeping into the same volume in a pressure filter with a 0.45 mm acetate membrane and a pressure of two bar. The pores of the membrane become rapidly clogged if the slurry contains colloidal ingredients. The settling of the flock is tested in a measuring cylinder, whereby the settling time and the volume to which the flock 25 settles are compared.

The following examples illustrate the preparation of cationic lignins from ultrafiltered black liquor.

Example 1 This example starts from the ultrafiltered fraction of black liquor (Metsä-Serla Oy), whereby lignin is first crosslinked with formaldehyde in three different ways and then the products are cationized. The initial situation is shown in Table 1.

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table 1

Initial situation for cross-precipitation and cationization of ultrafiltered black liquor 5 _ _Grams Mole- Wet Dry Dry Mole ratio

Lignin 10 In ultrafiltered black liquor dry matter (ka) 18.6% 100 18.6 Organic matter 15 88.6% lane 16.5

Reagent GTAK-HCl 53.3%, MP 188.1 48.58 21.63 0.115 l

NaOH

20 In black liquor (11.4%) 2.12

Dry matter: 42.8 X 100 = 27.9% 25 153.58

Added (as 5 M solution) 1st batch 3 ml 0.60 2nd batch 10 ml 2.00 30 Total 13 4.72 0.118 1.03

The amount is 153.58 42.85

The first batch of NaOH was added before crosslinking, the second batch after crosslinking.

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Cross-linking was performed in a water bath in three 200 ml centrifuge tubes with high agitation. To the tubes were added 100 g of ultrafiltered black liquor (ca. 18.6%) and 3 ml of 5 N NaOH and 0.6, 1.0 and 5 ml of 37% HCHO solution and the reaction mixture was stirred at 95-100 ml. At 1.5 ° C. Calculated per 100 g of lignin, the formaldehyde concentrations in moles were 0.049, 0.081 and 0.121, respectively.

For cationization-cooled reaction mixtures containing cross-linked lignin, 10 ml of 5 N NaOH (2 g, 0.05 mol) and 21.63 g of GTAK-HCl reagent as a 53.3% aqueous solution were added. The reaction time at 55 ° C was 6 hours. The reaction was quenched by neutralizing the mixture with dilute hydrochloric acid. Nitrogen percentages were determined from the ultrafiltered and dried products to give a yield of 32% for reagent consumption in all crosslinking / cationization experiments. The low yield can be attributed to the hydrolysis side reaction during both reagent preparation and cationization. It can be seen from Table 2 that cross-linking of alkali lignin with formaldehyde prior to cationization actually causes a decrease in the optimal dosage in the vessel test. Experiments with a dispersion analyzer show cross-linking to improve flock durability (compare 25 relative floc sizes at different agitation rates). The commercial Fennopol 194 K used in the experiment is a strongly cationic polyacrylamide with a molecular weight of about 4 million.

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Table 2

Effect of alkali lignin CH 2 O crosslinking on the silica precipitation efficiency of the corresponding cationic lignin in ast iatest tests <a 5 _

Crosslinking Dosage <b Relative flocculent size (c degree, moles% N (a% silica 64 rpm 200 rpm 300 rpm ch2o / ioo g 10 0 2.3 0.041 0.65 0.37 0.10 0.049 2.3 0.041 0, 82 0.38 0.10 0.081 2.3 0.039 0.99 0.45 0.10 0.121 2.3 0.030 1.6-2.0 0.87 0.20

Fennopol 194 K

0.033 1.8-2.2 1.20 0.38 e) The crude product was purified by ultrafiltration through a Diaflo YM2 membrane (Amicon Corp., exclusion limit 1,000). In vessel tests, the standard colloidal dispersion was 20 microcrystalline silica (Min-U-Sil 5; Pennsylvania Class and Sand Corp.) at a concentration of 250 mg / 600 mL.

c) Relative floc size was determined with a photometric dispersion analyzer (PDA 2000 / Rank Brothers Ltd).

Example 2 This example demonstrates that cationic lignin with a nitrogen content (purified) of 3.0% and a reagent yield of 52% can be prepared from ultrafiltered black liquor with GTAK reagent. The cationic lignin thus prepared precipitated colloidal silica more efficiently in a vessel test than the commercial Fennopol K 1912 (a slightly cationic polyacrylamide-type polyelectrolyte having a molecular weight of about 4 million). The experiment used ultrafiltered black liquor (re-35 tentate) from Met-sä-Serla Oy with a dry matter content of 16.6%. The black liquor was evaporated at 90 ° C in an oven until the dry matter content was 29.9%.

Table 3 5 Preparation of cationic lignin from ultrafiltered black liquor with glycidyltrimethylammonium chloride (GTAK) reagent 10 Grams Mole-Wet Dry Mole ratio Baseline Starting mixture

Ultrasuod. black-dry-liquor, also 29.9% 604.1 180.1 content was 43.3%

Lignin 163.08

Reagent 228.8 151.47 0.999 1 GTAK, including 79% 100% epoxy epoxy 66.2% of 20 crude products 83.8% karst

NaOH 17.87 0.447 0.447

Reacted for 4 h at 35-40 ° C and then for 45 h at 55 ° C The purified product contained 3.0% nitrogen, resulting in a reagent yield of 52%.

Example 3 This example describes experiments in which solids and phosphorus were removed from the water leaving the post-clarification plant of Metsä-30 pulp Oy's Äänekoski mills biological treatment plant. The experiments were performed in a vessel test apparatus (Phipps & Bird) in which 600 ml of effluent was added to 800 ml beakers. Precipitators were added during rapid stirring (64 rpm), after which stirring was continued for 5 min. Before settling, the precipitate was stirred slowly for 5 minutes (30 rpm), after which the precipitate was allowed to settle without stirring for 30 minutes. After 30 minutes, a 100 ml sample of the clarified solution was pipetted. All chemical doses are calculated per liter of 5 wastewater (ppm, mg / l, g / m3).

Experiments 1 and 3, respectively, show that the reduction in phosphorus content at the dose of 37.5 ppm for Ansu 2 (commercial aluminum sulphate, manufactured by Kemira Oy) and 1.25 ppm for cationic lignin is of the same order of magnitude (49% vs. 59%) and the reduction in solids content is greater pi (81% vs. 68%) than Ansu 2 at 35 ppm and cationic Fennopol at 2.2 ppm.

In Experiments 5, 6 and 7, in which Fe 3 * sulphate was used in combination with cationic lignin, the amount of phosphorus 15 could be reduced by the same amount as in Experiment using Ansu 2 and cationic lignin, respectively (Experiment 1). Although the deposition of ilok was promoted by neutral Fennopol N-300 (a very slightly anionic polyacrylamide with a molecular weight of about 10 million), 20 solids could be significantly reduced only in Experiment 4 (85%), in other experiments containing Fe3 + sulphate (5, 6 and 7) less than 50%.

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Table 4

Removal of phosphorus and colloidal solids from pulp mill effluent at pH 7.5 using co-dosing of inorganic coagulant and cationic lignin or cationic poly (acrylamide) or neutral poly (acrylamide)

Experiment Inorganic Cationic Reduction% 10 No. coagulant polyelectro-phosphorus (ppm) lithium (ppm) substance

Ansu 2 cat. lignin 1 37.5 1.25 81 49 15 2 37.5 3.75 80 52 cat. Fennopol 3 35 2.2 68 59

Fe3 + sulfate cat. Fennopol lignin N-300 20 4 31.3 1.56 - 85 54 5 31 1.25 1.25 40 58 6 31 1.90 1.90 40 58 7 31.3 1.56 1.90 48 58 25 Pulp mill the effluent contained 0.95 mg / l phosphorus and 97 mg / l solids. The solution for Experiment 1 contained 3 g of Ansu 2 and 100 mg of cationic lignin per liter of water. In Experiment 2, the precipitation solution contained 3 g of Ansu 2 and 300 mg of cationic lignin per liter. Experiment 3 used a solution 30 containing 5 mg of ferric. sulfate and 0.25 mg of cationic lignin. Ferrisulfate was commercial (70%) and dried in an oven at 120 ° C to constant weight.

Example 4 This example describes how, after crosslinking from ultrafiltered black liquor with GTAK-HCl reagent, cationic lignin is obtained in a reagent yield of 73.6%.

Table 5 5 Conditions for Cross-linking and Cationization of Ultrafiltered Black Liquid with GTAK-HCl Reagent-Grams_ Moles 10 Wet Dry Moles Ratio

Lignin

In ultrafiltered black liquor, 15 ka 27.5% 986 271.2

Organic part 241.4

NaOH (M 40.01) in black liquor 29.8

Additions 20 1-batch (before cross-linking) 13.8 2-batch (after cross-linking) 23.0 1.665 1.68

Crosslinking 80 ° C / 6 h Formaldehyde (M 30.02) 37% solution 50 18.5 0.616

Etherification 65 ° C / 6.5 h GTAK-HCl (M 188.11) 62.3% solution relative to the active substance 300 186.9 0.994 l

The dry matter was 28.9% when crosslinked and 38.4% when etherified. The reagent in the reaction mixture was 0.994 / 241.4 x 100 = 0.412 mol / 100 g of lignin. Formal-35 dehyde was used in 0.26 moles per 100 g of lignin.

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For crosslinking, the formaldehyde was mixed with alkali lignin at 50 ° C, after which the temperature was raised to 80 ° C and the mixture was stirred at this temperature for 6 hours.

To the cooled mixture at 65 ° C was added a second portion of NaOH and the cationization reagent with stirring over 0.5 h. Stirring was continued at the same temperature for 2.5 hours, at which time the reaction mixture was completely soluble in water. The reaction was allowed to proceed at 65 ° C for 3.5 hours, after which the mixture was neutralized with dilute hydrochloric acid. The ultra-filtered (Amicon PM 10 membrane, M> 10,000) and dried sample contained 2.9% nitrogen.

Calculation of reagent yield: per 100 g of pure cationic lignin was. 0> 20vl4 x 152j64 = 31.62 g of 15 14 GTAK reagent and 100.00-31.62 = 68.38 g of lignin. Reagent yield: 0.207 241.4 = 73 5% 68.38 0.994

Claims (3)

91642 Patent Claims Cationic lignin useful as a flocculant, characterized in that it is prepared from an ultrafiltered fraction of 5 black liquors by first ultrafiltrating the black liquor, followed by cationization of the resulting ultrafiltered fraction with glycidyltriammonium chloride or N- (3-chloro-2-hydroxypropyl) trim. chloride. Cationic ligin according to Claim 1, characterized in that the ultrafiltered fraction of the black liquor is crosslinked with formaldehyde before cationization. Process for the treatment of waste water, characterized in that the waste water is treated with a cationic lignin according to claim 1 or 2. il 91642